YEAST WILL LAST LONGER IF KEPT IN THE REFRIGERATOR

Q-My mother-in-law questioned me about my keeping yeast in the refrigerator. She reasons that the fridge is probably damp, and yeast should be kept in a cool, dry place. Where should I store it?

A-Yeast comes in two forms-compressed yeast, which is the small, solid cake, or active dry yeast, which usually comes in moisture-proof packages. The compressed yeast cake must be kept in the refrigerator. How long it will last depends on how fresh it is when you buy it. You should buy only enough for a particular purpose and use it as soon as possible, up to two weeks. After that it may not work. You can also freeze it and it will keep from two to six months.

The active dry yeast, if it`s in the airtight packages, doesn`t have to be refrigerated, but it will probably last longer if it is. The moisture in the refrigerator won`t affect it if it`s unopened. If you bought a 1-pound can of it, divide it up and freeze it.

To test the vitality of active dry yeast, Howard Hillman in ''Kitchen Science'' (Houghton Mifflin, $7.95) suggests you do the following: ''Just before using the yeast, mix some into 1/4 cup of lukewarm water that has been enriched with a 1/4 teaspoon of sugar, the food for the yeast. If the yeast mixture does not start to bubble within 5 or 10 minutes, your microorganisms are dead and will not leaven your dough or batter.''

Q-I read that clarified butter has no cholesterol. Is this true?

A-No. When you melt butter, you will notice that some sediment falls to the bottom and clearer oil is on the top. When you separate the clearer oil from the sediment, you have clarified butter. The sediment consists of milk solids, while the oil on top is almost pure butter fat. The cholesterol is in the butter fat.

Butter is clarified for use in certain recipes. You can fry with it at a much higher temperature before it starts to smoke. It is the milk solids that make butter scorch easily and they have been removed. Clarified butter also has a longer storage life. Butter that is superclarified, known as ''ghee'' in India, can be stored at room temperature for months.

If you clarify butter for any reason, don`t discard the milk solids. This sediment has practically no cholesterol, a lot of protein and has a buttery taste. You can use it as a spread.

READER FEEDBACK

Georgia Egeland, Missoula, Mont.: ''You mentioned in your column that bugs usually get into flour and cereal after they leave the mill. A friend showed me bugs in her flour that were not there a few weeks before. She brought the flour back to the store and the manager told her he had had other complaints. After some investigation, the store changed the sacks of flour to a section at least three aisles away from the bags of dry pet food. They had discovered that the bugs were rampant in the dry dog food and migrated to the flour.

''The manager asked my friend if she owned a dog and she said yes. And where did she keep the dog food? In the same cupboard as the flour. So he told her never to keep dry pet food in the same cabinet with flour and cereals. Hope this sheds some light on the problem.''

As soon as I read your letter, I moved a bag of dry cat food out of the kitchen and put it on a shelf in the hall closet.

The next day I read a letter from Fred Schumacher, a former president of a milling engineering company. Having received more complaints from readers about bugs in flour, cereal and vanilla powder, I had asked him if it would do any good to put these items in the freezer for a while when you get them home from the store. The answer is yes, particularly if the product is of a small quantity and remains in the freezer for several days.

I took the dry cat food out of the hall closet and put it in the freezer for two days. I`ve never had bugs in my pantry, but why push my luck?